In an RD converter (resolver/digital converter) that receives detected two-phase signals supplied by a resolver in order to calculate the rotation angle information of the resolver, two-phase pulse signals, which are an A-phase pulse signal and a B-phase pulse signal, are used as an output form of the rotation angle information. These two pulse signals are collectively referred to below as A/B-phase pulse signals.
FIG. 4 illustrates a conventional structure of this type of RD converter that outputs rotation information as A/B-phase pulse signals. An A/D converter (analog to digital converter) 11 converts detected two-phase signals (sin θ, cos θ) supplied by the resolver into digital values and inputs them to a CPU 12 (central processing unit). CPU 12 computes a rotation angle θ at intervals equal to a specified unit time based on the digital values of the detected two-phase signals, calculates an angle increment Δθ, which is the difference between the previous rotation angle θ and the calculated rotation angle θ obtained after the specified unit time, and gives the angle increment Δθ to a pulse output circuit 13.
Pulse output circuit 13 follows the timing of a clock signal CLK (not shown) to generate the same number of a sequence of up-count pulses UPCP or down-count pulses DWNCP as the value of the given angle increment Δθ depending on the rotation polarity of Δθ, and gives the sequence of pulses to an up/down counter 14. Up/down counter 14 counts up or down the pulses depending on which of the up-count pulses and down-count pulses were received. Next, the least significant bit of the count value of up/down counter 14 is exclusive-ORed (XORed) with the second least significant bit by XOR circuit 15 to generate an A-phase pulse signal and the second least significant bit is output as a B-phase pulse signal, so that two-phase pulse signals (for example, see patent literature 1) are obtained, which are to be supplied to an upward system not shown in the drawings.    Patent literature 1: Japanese Patent Application Laid-Open No. 2001-317962